Pat - as we have discussed, these changes will be discussed on the
webont mailing list - those interested in this discussion can follow
it there, as it is a public mailing list.
thanks
Jim Hendler
At 19:31 -0500 5/9/03, pat hayes wrote:
The relationships between OWL Full, OWL DL and OWL Lite could be
brought into somewhat sharper focus by some changes to the wording in
the document. I would suggest the following changes.
-----
1. Introduction, second para, remove needless judgemental prose and
clarify the relationships more explicitly:
"This document contains two formal semantics for OWL. One of these,
defined in Section 3 , is a direct model-theoretic semantics for the
abstract syntax, which applies to OWL DL and OWL Lite. The other,
defined in section 5, is a vocabulary extension of the RDFS semantics
[RDF MT] which applies to OWL Full. The first semantics is simpler,
but does not apply to cases which are excluded by the abstract
syntax, such as where classes need to be treated as individuals. We
show that the two semantics align naturally on the subset of OWL-RDF
graphs which conform to the abstract syntax under the translation in
section 4.
Appendix A...."
later:
"For such OWL ontologies the direct model theory is authoritative and
the RDFS-compatible model theory is secondary. "
change to:
"We believe that for such OWL ontologies, the two semantic
descriptions define the same entailments. In case any divergences are
found, however, the direct semantics should be taken to be normative
for OWL DL and OWL Lite ontologies."
Acknowledgements: DAM+OIL -> DAML+OIL
-----
Section 2., first sentence, following "and thus..": . Either omit, or
expand on what is meant by "facilitates access to"
In general, throughout this section, "OWL" is used without
qualification to refer to OWL DL, which is potentially misleading to
the reader, particularly in a separated document of this kind. I
suggest replacing "OWL" with "OWL DL" throughout this section.
"(Note, however, that both ... and ... do not provide..." / "(Note,
however, that neither ... or ... provide ... "
Similarly, references to what cannot be done in "an ontology" in
section 2.1 should be clarified, eg "A URI reference cannot be both
a datatypeID and a classID in an ontology "/ "...in an OWL DL
ontology".
This may require some extensive massaging of the text in section 2.1,
which in any case contains many partial truths and unclear statements.
The usage of "class" and "set" in this section should be clarified
and made rigorous. If this text is written under the assumption that
class names denote sets, it would be helpful if this were stated
clearly, preferably at the beginning of section 2, and an explicit
contrast drawn with RDF/S. (I can provide anchors in [RDF MT] to a
brief discussion of the issue if that would be helpful.)
"The class with identifier owl:Nothing is the empty class."
If 'class' here refers to the RDFS sense, there may be many empty
classes. Suggest change to "an empty class", or "the empty set".
" In OWL, as in RDF, a datatype denotes the set of data values that
is the value space for the datatype. Classes denote sets of
individuals. "
This is not quite accurate. The datatype URIref in RDF denotes the
datatype: the class extension is the set of data values. Also,
classes do not denote.
"Ontology annotations that use owl:imports have the extra effect of
importing the target ontology." This does not explain what is meant
by "importing". As it stands it conveys almost no information; a
brief explanation would be useful.
The discussion of 'names' of an ontology should make no reference to
the use of URIs in web access. The names of ontologies in the
abstract syntax have no connection to any Web construct, as is made
clear by the discussion of 'web-compatible' later in section 5. An
explicit statement to that effect would clarify this section, eg
(suggestion only)
"The abstract syntax assumes that every ontology has a name. The
obvious intended purpose of this is to provide a means to refer to,
and hence access, a document containing a version of the ontology in
some communicable syntax; but at this abstract level, the
relationship between an ontology and its name is considered purely
platonic. We will return to this matter when discussing OWL-RDF
ontologies as entities which can be denoted by URIs. "
-----
Section 3, first paragraph, suggested rewrite:
"This semantics is a conventional model theory attached to the OWL
abstract syntax, and therefore applies only to OWL DL and OWL Lite.
It differs from the RDF semantics in several respects. It interprets
class and property names extensionally, uses a nonstandard
interpretation of rdf:type and differs slightly in its treatment of
typed literals. The semantics for OWL Full in section 5 is more
complicated, but is fully consistent with the RDFS semantics."
-----
Pat (Wearing no hats, for once.)
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